(I posted this on my blog to keep up with my Iron Man quota, but since I got no comments there, I decided to re-post it here where I know people enjoy a good Perl puzzle.)

I'm working on a longer article about version numbers in Perl, why there are now so many ways to screw them up, and some recommendations. In the meantime, I realized that some of my examples for that article might be a fun puzzle for others with some curiosity and time to kill.

Format

Each puzzle consists of the output of several Perl one-liners using different versions of Perl. They are run in a directory with a single file, Foo.pm, like this:

package Foo; 
use strict; 
use warnings; 
our $VERSION = 1.23; 
1;
[download]

In each puzzle, line 4 (the $VERSION line) is different and the puzzle is to figure out the $VERSION line given only the sample output.

Puzzle 1

$ perl5.10.0 -e 'use Foo 0.001001'

$ perl5.8.9 -e 'use Foo 0.001001'
Foo version 0.001001 required--this is only version 0.001001 at -e lin
+e 1.
BEGIN failed--compilation aborted at -e line 1.

$ perl5.8.9 -Mversion -e 'use Foo 0.001001'
[download]

Puzzle 2

N.B. This puzzle intentionally requests a higher version number than is in Foo.

$ perl5.10.0 -e 'use Foo v0.1_1'
Foo version v0.1_1 required--this is only version v0.0_1 at -e line 1.
BEGIN failed--compilation aborted at -e line 1.

$ perl5.8.0 -e 'use Foo v0.1_1'
Foo version v0.1.1 required--this is only version v0.0.1  at -e line 1
+.
BEGIN failed--compilation aborted at -e line 1.

$ perl5.6.2 -e 'use Foo v0.1_1'
Foo version 0.011 required--this is only version 0  at -e line 1.
BEGIN failed--compilation aborted at -e line 1.
[download]

Puzzle 3

$ perl5.10.0 -e 'use Foo 0.000001'
Foo version 0.000001 required--this is only version v0.0_1 at -e line 
+1.
BEGIN failed--compilation aborted at -e line 1.

$ perl5.10.0 -e 'use Foo v0.0_1'

$ perl5.8.9 -e 'use Foo v0.0_1'

$ perl5.8.0 -e 'use Foo v0.0_1'
Foo version v0.0.1 required--this is only version v0.0_1  at -e line 1
+.
BEGIN failed--compilation aborted at -e line 1.

$ perl5.6.2 -e 'use Foo v0.0_1'
Foo version 0.001 required--this is only version v0.0_1  at -e line 1.
BEGIN failed--compilation aborted at -e line 1.
[download]

Puzzle 4

$ perl5.10.0 -e 'use Foo v0.1.1'

$ perl5.8.9 -e 'use Foo v0.1.1'

$ perl5.10.0 -e 'use Foo v0.2.1'
Foo version v0.2.1 required--this is only version v0.1.1 at -e line 1.
BEGIN failed--compilation aborted at -e line 1.

$ perl5.8.9 -e 'use Foo v0.2.1'
Foo version 0.002001 required--this is only version 0.001001 at -e lin
+e 1.
BEGIN failed--compilation aborted at -e line 1.
[download]

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